Pin plate arrangement for a piano

ABSTRACT

A pin plate arrangement for a piano comprises plural layers of wooden members and an adhesive agent bonding the adjacent ones of the layers to each other, the adhesive agent consisting of a prepreg film impregnated with a thermosetting resin adhesive. The pin plate arrangement is kept for a long period of time having a less and constant moisture content and a smaller drop in the pinholding power.

United States Patent [1 1 ()kugawa et a1.

5]March 20, 1973 [54] PIN PLATE ARRANGEMENT FOR A PIANO [7 5] inv'eniifi'fasiiihimie Olrngawa; Rune Nagai,

both of Hamamatsu,Japan 7 3 Assigneez ii'p bf Seize Kabushiki Kaisha, Hamamatsu-shi, Japan [22] Filed: March 10, 1971 [21] App]. No.: 122,677

[30] Foreign Application Priority Data March 12, 1970 Japan ..45/20658 [52] US. Cl. ..84/186 WP [51] Int. Cl. ..Gl0c 3/04 [58] Field of Search ..84/184-188, 197, 84/200, 452

[56] References Cited UNITED STATES PATENTS 3,322,587 5/1967 Burnet et a1 ..156/216 3,551,272 12/1970 Ash ..161/164 1,212,775 1/1917 Kantor 1,264,140 4/1918 Bayer..... 2,339,752 I/ 1944 Bilhuber. 3,433,111 3/1969 Kanda ..84/188 FOREIGN PATENTS OR APPLICATIONS 526,130 6/1956 Canada ..84/188 Primary Examiner-Richard B. Wilkinson Assistant Examiner-Lawrence R. Franklin Attorney-Flynn & Frishauf [57] ABSTRACT A pin plate arrangement for a piano comprises plural layers of wooden members and an adhesive agent bonding the adjacent ones of the layers to each other, the adhesive agent consisting of a pre-preg film impregnated with a thermosetting resin adhesive. The pin plate arrangement is kept for a long period of time having a less and constant moisture content and a smaller drop in the pin-holding power.

6 Claims, 7 Drawing Figures PATENTED R I975 SHEET'IUF 2 F I 2 PFIOR ART FIG.3

FIG.4

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5 INTERIOR MOISTURE CONTENT (/o) m w m m @L mumom 02540:

2E 4 no ZOrEDZwFbN PATENTEU MR 2 I975 SHEET 2 0F 2 ATTENUATION (PERCENTAGES) A 1 A O O 0 6 O 26 9: more @256:

DRYING PERIOD (DAYS) FIG.7

PIN PLATE ARRANGEMENT FOR A PIANO BACKGROUND OF THE INVENTION:

The present invention relates to a pin plate arrangement for a piano and more particularly to improvements in a pin plate arrangement for a piano which conventionally consists of laminated wooden plates.

A piano is generally so designed as to produce a sound of a predetermined tone pitch when selective depression of any of a plurality of keys juxtaposed in the order of musical notes causes the corresponding string or strings to be struck by a hammer. The string or strings are supported at one end by hitch pins embedded in a piano frame and at the other end by tuning pins embedded in the undermentioned pin plate (or wrest-plank).

There is disposed a pin plate 12, as shown in FIG. 1, on the inside of a piano frame 11 open at the bottom and assuming a channel shape in section. One end portion of the piano frame 11 is bored with through holes 14 at a point facing one end of a string 13 corresponding to each key, the other end of which is supported by the aforesaid hitch pins (not shown). Those parts of the pin plate 12 which face the through holes 14 are perforated with a plurality of pin support holes 15 having a suitably smaller diameter than the through holes 14. into the pin support holes 15 are forcedly inserted under pressure a plurality of tuning pins 16 (hereinafter simply referred to as the pins") through the corresponding through holes 14. Those portions of the pins 16 which project above the surface of the frame 1 1 support the end of the corresponding string 13. In this case, the outer periphery of that part of each pin 16 inserted into the through holes 14 is covered with a ring bush 17.

When the pin 16 is inserted into the support hole 15 and the string 13 is attached to the head of the pin under tension, the pin is subjected not only to a tension force acting in the direction in which the string is stretched but also to a twisting force acting in a certain direction especially when the string is struck by a hammer. For this reason, the pin plate arrangement should always exert a sufficient frictional force to the pin so as to prevent it from turning or tilting from a predetermined position due to the aforementioned external forces. The torque of the pin is usually set to be about (l20i60) Kg/cm but may be about 50 Kg/cm at a minimum. To this end, material for the pin plate should provide over a long period of time a proper degree of compressibility and elasticity. Heretofore, a wooden pin plate has been favorably accepted taking into account various factors such as the aforesaid strengthwith which the pin plate is desired to hold the pins, and the economy and mass production of the plate.

Namely, a pin plate arrangement prepared from relatively hard wood, for example maple, has compressibility and elasticity equal to about l/lO of those of plastic materials and about l/lO of those of metals, which are measured in a direction perpendicular to the grain direction, so that when the pin is inserted into the support hole 15 under pressure, the inner wall of the hole 15 is suitably deformed due to compression, but immediately regains an adequate degree of elasticity to be pressed against the outer periphery of the pin 16, thereby supporting it with a sufficient pin-holding power.

Since, however, wooden material generally tends to expand or contract due to variations in interior moisture content, the wooden pin plate arrangement has the drawback that its power to hold the pin varies with changes in the moisture content.

Namely, for instance, when interior moisture content decreases, the wooden plate contracts to broaden the diameter of the pin support hole. As a result, the frictional force applied by the pin plate arrangement to support the pin is reduced, causing the pin to turn and thereby to slacken the tension of the string. If, under such condition, the key is depressed, the tone derived from the corresponding string or strings will present an improper pitch.

Conversely when interior moisture content increases, the wooden plate swells to contract the pin support hole. Although, in this case, there seems to be no problem due to the pin plate arrangement applying a greater frictional force to the pin, the wooden plate presents different degrees of expansion between those parts thereof facing the top and bottom of the pin support hole, probably because the plate arrangement is fixed to the piano frame 11 (or permissibly a suitable support rod), as shown in P10. 1, only alongthe entire side periphery and at the top. This event often leads to cracks in the inner wall of the pin support hole, reducing the frictional force of the pin plate arrangement supporting the pin, as in the preceding case.

To reduce variations in the aforementioned frictional force applied on the pins by a pin plate, it is important that the moisture content of the pin plate be minimized as far as possible. The magnitude of the frictional force or pin-holding power is greatly affected by the moisture content of the pin plate or the degree to which it is dried when it is perforated with pin support holes.

It is well known that the pin plate dried to the extent of about 6 percent moisture content has the strongest frictional force.

FIG. 2 is a perspective view of the construction of a prior art pin plate arrangement for a piano.

The pin plate arrangement of FIG. 2 is prepared by integrally laminating plural sheets 21a, 21b, 21c of substantially rectangular hard wooden material such as maple sheets, having a proper thickness (generally 5 to 8 mm), by applying water-soluble adhesive agents 22a, 22b such as milk casein glue to the interfaces of the sheets.

With the conventional pin plate arrangement for a piano of the aforesaid construction, however, the moisture contained in the water-soluble adhesive agents 22a, 22b invades the component sheets of the arrangement when they are bonded together.

Further there occurs a gradient in the distribution of moisture content at the peripheral and central parts of the arrangement. Accordingly, the prior art pin plate arrangement has the drawback that it must be subjected to forced drying for a considerable period of time (generally two to three months) after the component sheets are bonded in order to attain a substantially uniform and adequate moisture content (about 6 percent) in the arrangement as a whole, thus requiring tremendous costs to store the arrangement while it is subjected to the forced drying and to install a drying apparatus.

it is, therefore, the object of the present invention to provide a pin plate arrangement for a piano so constructed as to eliminate the necessity of being subjected to force drying after its component sheets are bonded and also capable of maintaining a substantially uniform and proper moisture content over a long period of time.

SUMMARY OF THE INVENTION According to an aspect of the present invention, there is provided a pin plate arrangement for a piano comprising plural layers of wooden members and an adhesive agent bonding the adjacent ones of the layers to each other, the improvement wherein the adhesive agent comprises a pre-preg film impregnated with a thermosetting resin adhesive.

BRIEF EXPLANATION OF THE DRAWINGS The present invention can be more fully understood from the following detailed description when taken in connection with reference to the accompanying drawings, in which:

FIG. 1 is a fragmentary sectional view of a prior art pin plate arrangement for a piano, showing a fundamental construction in use;

FIG. 2 is a perspective view of the prior art pin plate arrangement for a piano;

FIG. 3 is a perspective view of a pin plate arrangement according to an embodiment of the present invention;

FIG. 4 is a fragmentary sectional view of the pin plate arrangement of FIG. 3 in use;

FIG. 5 is a graphical comparison between the interior moisture content and attenuation of a pin-holding force of a pin plate arrangement according to the invention and those of the prior art;

FIG. 6 is a graphical comparison between the variation in the pin-holding force ofa pin plate arrangement according to the invention and that of the prior art; and

FIG. 7 is a perspective view of a pin plate arrangement for a piano according to another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

FIG. 3 is a perspective view of a pin plate arrangement for a piano according to an embodiment of the present invention. According to this embodiment, plural layers of relatively thick wooden plates comprise, for example, five layers 31a, 31b, 31c, 31d and 31s of wooden material each about 4 to mm thick cut out of, for example, maple. In this case, the grains of the adjacent layers 31a to 31e preferably intersect each other substantially at right angles as shown in FIG. 3.

The respective wooden plates 31a to 31e are dried in advance to about 5 to 7 percent moisture content and under this condition bonded together with a hot press by inserting prepreg films or sheets 32a, 32b, 32c and 32d uniformly impregnated and coated with, for example, a thermosetting phenolic resin adhesive between the wooden plates 31a to 3le. Such thermosetting phenolic resin is commercially available under the trade name Sumilite Resin PR 50338."

The aforementioned bonding operation was carried out under the following conditions.

Temperature Time Drying condition Bonding condition One end portion of the pin plate arrangement 33 for a piano manufactured as described above, as shown in FIG. 4, is perforated with a plurality of pin support holes 41 each having a slightly smaller diameter than that of a tuning pin 42 for supporting the end of a string 43. The pins 42 are inserted into the holes 41 under pressure in the following manner. The pin plate arrangement 33 is fixed, for example, to the inner wall of a piano frame 44 open at the bottom and assuming a channel shape in section. The upper wall of the frame 44 facing the pin support holes 41 is bored with through holes 45 having suitably larger diameters than the pins 42. The pins 42 are inserted into the through holes 45 and further into the pin support holes 41, for example, by an air hammer, the ends of the corresponding strings 43 being supported by the head portions of the pins 42 which project-above the frame 44. Thereafter the pins 42 are turned by a tuning hammer so as to obtain a sufficient tension in the strings 43.

As mentioned above, the layers 31a to 31e between the respective wooden plates according to the pin plate arrangement of the invention are thermally bonded by using the prepreg films 32a to 32d impregnated with a thermosetting resin adhesive, which contain little or no moisture. Accordingly, atmospheric moisture as well as the moisture in the adhesive agent does not intrude into the respective wooden plates or layers 31a to 31e, permitting the moisture content of the laminated assembly as a whole to be maintained at an extremely low level. This eliminates the necessity of subjecting the assembly to forced drying after bonding as has been required for the prior art pin plate arrangement, thereby reducing manufacturing cost.

Further, as compared with the prior art, the pin plate arrangement of this invention more effectively prevents the respective wooden plates 31a to 31e from being affected by atmospheric humidity, no matter how it varies, due to the presence of the aforesaid pre-preg films 32a to 32d substantially enclosing the wooden plates 31a to 31e. As a result, since the expansion and contraction of the wooden plates 31a to 31e caused by variations in ambient atmosphere as well as the moisture contained in the adhesive agent is more reduced than has been possible in the past, the pin plate arrangement of the invention applies a substantially constant frictional force to the pins 42, thereby effectively preventing the disorderly tuning of the strings 43.

When pressed under heat, the thermosetting resin adhesive coated on the films 32a to 32d passes into the wooden plates 31a to 31e to reinforce their fibrous tissue, prominently minimizing the occurrence of cracks around the pin support holes 41 as has often been observed in the past with prior art devices.

FIG. 5 is a graphical comparison between the interior moisture content pin-holding force attenuation of a pin plate arrangement according to the invention and those of the prior art. The point 51 of FIG. 5 denotes the interior moisture content and pin-holding force attenuation of the pin plate arrangement of the invention constructed as shown in FIG. 3, and the points 52, 53 and 54, respectively, show the interior moisture contents and pin-holding force attenuations of the prior art pin plate arrangements.

FIG. 6 is a graphical comparison between the variation in the frictional force of a pin plate arrangement according to the invention and that of the prior art.

The curve 61 of FIG. 6 denotes the property of the pin plate arrangement 33 of the invention constructed as shown in FIG. 3 (consisting of five wooden plates each about 6 mm thick and one wooden plate about 12 mm thick), and the curve 62 shows the property of the prior art pin plate arrangement constructed as shown in FIG. 2 (consisting of five wooden plates each about 6 mm thick and one wooden plate about l2 mm thick). As is apparent from FIG. 6, the pin plate arrangement of the invention not only has had a greater frictional force with respect to the tuning pins than the prior art, but also presents a smaller attenuation or decrease in the frictional force under a drying condition of 35C and 20 percent of relative humidity conducted for a predetermined number of days. After lOO-day drying, the pin plate arrangement of the invention exhibits only about 36 percent of attenuation or decrease in the frictional force, whereas the conventional type exhibits an attenuation of as large as 50 percent.

FIG. 7 illustrates another embodiment of the present invention wherein each layer of 31a to 31:; consists of a plurality of elongated wooden strips 311, 312, 313 connected together side by side with a thermosetting resin adhesive agent or a pre-preg film uniformly impregnated and coated with a thermosetting phenolic resin adhesive.

The wooden strips 311, 312, 313 constituting one layer have grains extending in the same direction. The wooden layers 31a to 31e are bonded together with pre-preg sheets or films 32a to 31d interposed therebetween, in the same manner as explained in the preceding embodiment. It will be apparent that such pin plate arrangement has the same effect as that of FIG. 3.

What we claim is:

1. A pin plate arrangement for a piano comprising plural layers of wooden members and an; adhesive agent bonding adjacent ones of said wooden layers to each other, the improvement wherein the adhesive agent comprises a dried pre-preg film or sheet impregnated with a thermosetting resin adhesive, said adhesive agent being dried before being bonded to said wooden members. i

2. The pin plate arrangement according to claim 1 wherein said each wooden member is dried in advance to have about 5 to 7 percent moisture content before bonding.

3. The pin plate arrangement according to claim 1 wherein each of said wooden layers comprises of a wooden plate of maple wood about 4 to 15 mm thick.

4. The pin plate arrangement according to claim 1 wherein said wooden layers comprise cross-grain plies of hard wood.

5. The pin plate arrangement according to claim 1 wherein each wooden layer comprises a plurality of elongated wooden strips connected together side by side, grains of the strips included in the same layer extending in the same direction.

6. The pin plate arrangement according to claim 1 wherein said adhesive is a phenolic resin. 

2. The pin plate arrangement according to claim 1 wherein said each wooden member is dried in advance to have about 5 to 7 percent moisture content before bonding.
 3. The pin plate arrangement according to claim 1 wherein each of said wooden layers comprises of a wooden plate of maple wood about 4 to 15 mm thick.
 4. The pin plate arrangement according to claim 1 wherein said wooden layers comprise cross-grain plies of hard wood.
 5. The pin plate arrangement according to claim 1 wherein each wooden layer comprises a plurality of elongated wooden strips connected together side by side, grains of the strips included in the same layer extending in the same direction.
 6. The pin plate arrangement according to claim 1 wherein said adhesive is a phenolic resin. 